Methods for producing a fluoroalkyl iodide by telomerization are known.
Such telomerization is conducted by consecutive reactions between 1-iodoperfluoroethane (C2F5I) as a telogen and tetrafluoroethylene as a taxogen in a reactor.
For example, Patent Literature (PTL) 1 discloses a process for producing a fluoroalkyl iodide represented by Rf—(CF2CF2)n—I (wherein Rf is a fluoroalkyl group having 1 to 6 carbon atoms, and n is an integer of 1 to 4) by telomerizing a compound represented by the formula Rf—I (wherein Rf is a fluoroalkyl group having 1 to 6 carbon atoms) as a telogen and tetrafluoroethylene as a taxogen in a reactor in which a catalyst is present.
While such a method is excellent, there is room, for improvement in terms of selectivity of the fluoroalkyl iodide produced. Specifically, telomerization is conducted by consecutive reactions; therefore, as the reaction of 1-iodoperfluoroethane (C2F5I) with tetrafluoroethylene progresses, the reaction of a telogen represented by the above formula wherein n is 1 or more with tetrafluoroethylene also proceeds. The rate of reacting 1-iodoperfluoroethane (C2F5I) with tetrafluoroethylene is slow; therefore, this reaction is a rate-determining step. Accordingly, while 1-iodoperfluoroethane (C2F5I) is reacted with tetrafluoroethylene to produce 1-iodoperfluorobutane (C4F9I), the obtained 1-iodoperfluorobutane (C4F9I) reacts with tetrafluoroethylene in the reactor, and consecutive reactions take place progressively. For example, when the desired fluoroalkyl iodide is 1-iodoperfluorohexane (C6F13I), many other fluoroalkyl iodides that have more carbon atoms than 1-iodoperfluorohexane (C6F13I) are also produced, which results in low selectivity of the desired fluoroalkyl iodide.
To solve this problem, a production method has been proposed in which 1-iodoperfluoroethane (C2F5I) is reacted with tetrafluoroethylene in a first reactor, after which 1-iodoperfluorobutane (C4F9I) is separated from the obtained reaction mixture and transferred into a second reactor, and tetrafluoroethylene is added thereto to allow a reaction for producing a fluoroalkyl iodide having more carbon atoms than 1-iodoperfluorobutane (C4F9I) to proceed in the second reactor (see, for example, Patent Literature (PTL) 2).
While such a method is also excellent, the method produces by-products represented by Rf—(CF2CF2)n—H (wherein Rf is any one of fluoroalkyl groups having 1 to 10 carbon atoms, and n is an integer indicating a degree of polymerization) due to the use of a peroxide as a catalyst for promoting the reaction, and the method requires a step of removing the by-products from the reaction system, which results in low production efficiency.
Thus, there is a need for a new method of producing a mixture of fluoroalkyl iodides with high production efficiency, the method enabling the production of a desired fluoroalkyl iodide with high selectivity.